1. Field of the Invention
This invention relates to a fluctuation torque cancellation apparatus which can be connected to a rotation shaft (i.e., an input shaft or an output shaft) of a motion conversion apparatus for converting a continuous rotational motion of the input shaft into a special rotational motion of the output shaft, such as an intermittent rotational motion and a swinging rotational motion, or a predetermined-type motion of the output shaft such as a combination of such rotational motions, and also can be connected to an input shaft of a pressing machine incorporating a motion conversion apparatus for converting a continuous rotational motion of the input shaft into a reciprocal linear motion of a slide.
2. Related Art
In a motion conversion apparatus for converting a continuous rotational motion of an input shaft into a predetermined-type rotational motion of an output shaft through a cam mechanism such as an intermittent indexing device, a torque, acting on the output shaft during the operation, varies continuously, and a reaction force of this torque acts as a fluctuation torque on the input shaft. This torque, acting on the input shaft, prevents a uniform rotation of the input shaft, and causes vibrations during the operation and an operation error resulting therefrom. The influence of this torque is great particularly during high-speed rotation of the apparatus, and therefore in order to achieve a high-speed design of the apparatus, it is necessary to suppress this fluctuation torque to a low level as much as possible.
In order to suppress this fluctuation torque, a fluctuation torque cancellation apparatus is proposed, for example, in Japanese Patent Unexamined Publication No. 60-4665. In this apparatus, a follower, to which a cam follower, engaged with a fluctuation torque-cancelling compensation cam mounted on a continuously-rotating shaft (e.g. a cam shaft), is fixedly secured, is reciprocally moved in accordance with a cam curve of the compensation cam, so that a coil spring, provided to urge or press the follower, repeatedly accumulates and releases energy in accordance with a torque fluctuation of the continuously-rotating shaft. More specifically, during a step in which the accumulated energy is released, there is produced a torque acting in a direction to assist the rotation of the continuously-rotating shaft, whereas during a step in which the energy is accumulated, there is produced a torque acting in a direction to prevent the rotation of the continuously-rotating shaft. With this operation, at an acceleration section at which the rotation tends to become low, the acceleration torque is promoted, whereas at a deceleration section at which the rotation tends to become high, the braking torque is promoted, and by doing so, the fluctuation torque can be suppressed to a low level, and the stable motion can be obtained.
However, the above conventional fluctuation torque cancellation apparatus with the mechanical spring, when mounted on the motion conversion apparatus, is usually used, considering the rotational speed (to be used) of a motion conversion apparatus body, and in some cases, the intended effects have not been obtained outside this predetermined rotational speed range. For example, in an apparatus which is designed for high rotational speed, and serves to cancel a fluctuation torque due to an inertia load, a cam curve is so determined that a very large cancellation torque can be produced during acceleration, and when this apparatus is used during low-speed rotation, the produced inertia load is smaller than during the high-speed rotation, and therefore the promoting torque of a level more than necessary is exerted during the acceleration, while the braking torque of a level more than necessary is exerted during deceleration, and in contrast with the intention, an unnecessary torque fluctuation is produced. And besides, when assembling such a fluctuation torque cancellation apparatus, the assembling operation must be effected while holding the coil spring in a considerably-compressed condition, which results in a problem that the efficiency of the operation is poor.